Flywheel systems

ABSTRACT

A flywheel system comprises a flywheel rotor comprising a rotor disc and a rotor shaft and has a longitudinal axis extending centrally through the rotor disc and the rotor shaft. The system further comprises a journal assembly configured to facilitate rotation of the flywheel rotor. The journal assembly comprises a sleeve having an aperture extending therethrough from a first end to a second, opposite end, a rod at least partially disposed within the aperture of the sleeve, and a nut coupled to a portion of the rod. The rod has a length greater than the sleeve such that a portion of the rod extends axially beyond the first end of the sleeve. A method of forming the flywheel comprises coupling the rod to the rotor shaft and pulling the second end of the rod to tension the rod. The nut maintains the tension in the rod when coupled thereto.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/074,239, filed Oct. 19, 2020, which will issue as U.S. Pat. No.11,680,624 on Jun. 20, 2023, which is a continuation of U.S. patentapplication Ser. No. 16/291,895, filed Mar. 4, 2019, now U.S. Pat. No.10,982,730, issued Apr. 20, 2021, the disclosure of each of which ishereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a flywheel energystorage system. More particularly, this disclosure relates to journalassemblies for supporting rotation of a flywheel rotor.

BACKGROUND

Energy can be converted from one form to another, such as fromelectrical energy into kinetic energy and vice versa. A flywheel is anenergy system that stores energy as rotational kinetic energy.Accordingly, electrical energy may be provided to a motor that can spina flywheel. The electrical energy may be received for storage in theflywheel. The momentum of the flywheel is a form of stored energy. Themotor can also be used as a generator and convert the rotational kineticenergy of the flywheel into electrical energy. Once a flywheel hasmomentum, the flywheel can theoretically spin indefinitely. However,parasitic losses such as friction and drag can diminish the efficiencyof a flywheel as an energy storage device. Accordingly, it can bedesirable to increase the efficiency of a flywheel energy storagesystem. Further, friction and drag can reduce the usable life of theflywheel system. By way of example, bearings, which support the flywheelfor rotation, may wear prematurely as a result of flywheel imbalancesduring operation.

BRIEF SUMMARY

Various embodiments of the disclosure comprise a flywheel systemcomprising a flywheel rotor comprising a rotor disc and a rotor shaft,the rotor having a longitudinal axis extending centrally through therotor disc and the rotor shaft. The system further comprises a journalassembly configured to facilitate rotation of the flywheel rotor. Thejournal assembly comprises a sleeve having an aperture extendingtherethrough from a first end to an opposite second end and alongitudinal axis of the sleeve extending therethrough from the firstend to the second end. The second end of the sleeve is coupled to therotor shaft. The journal assembly further comprises a rod at leastpartially disposed within the aperture of the sleeve. A first end of therod extends axially beyond the first end of the sleeve and a second endof the rod is coupled to the rotor shaft. A longitudinal axis of the rodextends therethrough from the first end to the second end wherein thelongitudinal axes of the sleeve and the rod are coaxial with thelongitudinal axis of the flywheel rotor. The journal assembly furthercomprises a retaining element coupled to the first end of the rodextending axially beyond the first end of the sleeve.

A method of using a flywheel system comprises rotating a flywheel rotordisposed between an upper journal assembly and a lower journal assembly.Each of the upper journal assembly and the lower journal assembly iscoupled to the flywheel rotor and comprises a sleeve having an apertureextending therethrough from a first end to an opposite second end, a roddisposed within the aperture of the sleeve such that a portion the rodextends axially beyond the first end of the sleeve, and a retainingelement coupled to the portion of the rod extending axially beyond thefirst end of the sleeve. The method further comprises lifting theflywheel rotor axially toward an upper bearing assembly and away from alower bearing assembly to apply an axially compressive force against abearing disposed within the upper bearing assembly. The upper bearingassembly is disposed about the upper journal assembly.

A method of forming a flywheel system comprises coupling a rod to aflywheel rotor shaft. The rod has a first end and an opposite end withthe first end of the rod coupled to the flywheel rotor shaft. A sleeveis disposed about the rod and coupled the sleeve to the flywheel rotorshaft. The sleeve has a first end and an opposite second end. The firstend of the sleeve is coupled to the flywheel rotor shaft. The second endof the rod extends axially beyond the second end of the sleeve. Themethod further comprises pulling the second end of the rod to tensionthe rod, and coupling a retaining element to the second end of the rodto maintain the tension in the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of thedisclosure, various features and advantages of embodiments of thedisclosure may be more readily ascertained from the followingdescription of example embodiments of the disclosure when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a flywheel energy storage system;

FIG. 2 is a partial view of a housing of the flywheel energy storagesystem of FIG. 1 ;

FIG. 3 is an enlarged cross-sectional view of an upper assemblyillustrating connection between a flywheel rotor and a motor and/orgenerator of FIG. 1 ;

FIG. 4 is an enlarged cross-sectional view of a lower assemblyillustrating connection between the flywheel rotor and a motor of FIG. 1;

FIG. 5 is a perspective view of a journal assembly of FIG. 1 ;

FIG. 6 is a perspective view of a rod of the journal assembly of FIG. 5; and

FIG. 7 is a perspective view of a sleeve of the journal assembly of FIG.5 .

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views ofany particular component, device, or system, but are merely idealizedrepresentations that are employed to describe embodiments of the presentdisclosure. The following description provides specific details ofembodiments of the disclosure in order to provide a thorough descriptionthereof. However, a person of ordinary skill in the art will understandthat the embodiments of the disclosure may be practiced withoutemploying many such specific details. Indeed, the embodiments of thedisclosure may be practiced in conjunction with conventional techniquesemployed in the industry. In addition, the description provided belowdoes not include all elements to form a complete structure or assembly.Only those process acts and structures necessary to understand theembodiments of the disclosure are described in detail below. Additionalconventional acts and structures may be used. Also note, any drawingsaccompanying the application are for illustrative purposes only, and arethus not drawn to scale. Additionally, elements common between figuresmay have corresponding numerical designations.

As used herein, the terms “comprising,” “including,” “containing,”“characterized by,” and grammatical equivalents thereof are inclusive oropen-ended terms that do not exclude additional, unrecited elements ormethod steps, but also include the more restrictive terms “consistingof” and “consisting essentially of” and grammatical equivalents thereof.

As used herein, the term “may” with respect to a material, structure,feature, or method act indicates that such is contemplated for use inimplementation of an embodiment of the disclosure, and such term is usedin preference to the more restrictive term “is” so as to avoid anyimplication that other compatible materials, structures, features andmethods usable in combination therewith should or must be excluded.

As used herein, the term “configured” refers to a size, shape, materialcomposition, and arrangement of one or more of at least one structureand at least one apparatus facilitating operation of one or more of thestructure and the apparatus in a predetermined way.

As used herein, the singular forms following “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

As used herein, spatially relative terms, such as “beneath,” “below,”“lower,” “bottom,” “above,” “upper,” “top,” “front,” “rear,” “left,”“right,” and the like, may be used for ease of description to describeone element's or feature's relationship to another element(s) orfeature(s) as the elements and features are illustrated and oriented inthe figures. Unless otherwise specified, the spatially relative termsare intended to encompass different orientations of the materials inaddition to the orientation depicted in the figures.

As used herein, the terms “longitudinal,” “longitudinally,” “axial,” or“axially” refers to a direction parallel to a rotational axis of one ormore components of the flywheel energy storage system described hereinincluding, but not limited to, the flywheel rotor described herein. Forexample, “longitudinal” or “axial” movement shall mean movement in adirection substantially parallel to the rotational axis of the flywheelenergy storage system as described herein.

As used herein, the terms “radial” or “radially” refers to a directiontransverse to a rotational axis of one or more components of theflywheel energy storage system described herein including, but notlimited to, the flywheel rotor described herein. For example, “radialmovement” shall mean movement in a direction substantially transverse(e.g., perpendicular) to the rotational axis of one or more componentsof the flywheel energy storage system as described herein.

As used herein, the term “substantially” in reference to a givenparameter, property, or condition means and includes to a degree thatone of ordinary skill in the art would understand that the givenparameter, property, or condition is met with a degree of variance, suchas within acceptable manufacturing tolerances. By way of example,depending on the particular parameter, property, or condition that issubstantially met, the parameter, property, or condition may be at least90.0% met, at least 95.0% met, at least 99.0% met, even at least 99.9%met, or even 100.0% met.

As used herein, “about” or “approximately” in reference to a numericalvalue for a particular parameter is inclusive of the numerical value anda degree of variance from the numerical value that one of ordinary skillin the art would understand is within acceptable tolerances for theparticular parameter. For example, “about” or “approximately” inreference to a numerical value may include additional numerical valueswithin a range of from 90.0 percent to 110.0 percent of the numericalvalue, such as within a range of from 95.0 percent to 105.0 percent ofthe numerical value, within a range of from 97.5 percent to 102.5percent of the numerical value, within a range of from 99.0 percent to101.0 percent of the numerical value, within a range of from 99.5percent to 100.5 percent of the numerical value, or within a range offrom 99.9 percent to 100.1 percent of the numerical value.

FIG. 1 is a cross-sectional view of a flywheel energy storage system100. The system 100 includes a housing 102 for enclosing a flywheelrotor 104. The rotor 104 comprises a rotor disc 106 and a rotor shaft108 having a central axis 112. The system 100 is configured such thatthe rotor 104 may rotate about the axis 112 in operation. Accordingly,the axis 112 may also be referred to herein as the rotational axis. Thesystem 100 is further configured to be axially translatable along theaxis 112 in operation. The rotor shaft 108 refers to a portion at and/oradjacent to a radial center of the rotor 104 and extending axiallybeyond the rotor disc 106. The rotor shaft 108 comprises an upper shaft108 a (FIG. 3 ) extending axially over an upper surface 103 of the rotordisc 106 and a lower shaft 108 b (FIG. 4 ) extending axially over alower surface 105 of the rotor disc 106. The upper shaft 108 a and thelower shaft 108 b may each comprise protruding (e.g., stepped) features107 a, 107 b (FIGS. 3 and 4 ), respectively, for coupling the rotor 104to an upper journal assembly 200 a (FIG. 3 ) and a lower journalassembly 200 b (FIG. 4 ), respectively. In some embodiments, an interiorof the housing 102 may be subject to a vacuum to reduce aerodynamic dragon the rotor 104 during operation.

The rotor 104 may be formed of a magnetic metal or metal alloy. Moreparticularly, the rotor 104 may comprise magnetic steel. In someembodiments, the rotor 104 is formed of 4340 steel. Other suitablematerials may include AISI 4330, 5330, 17-14PH (precipitation hardened),M300, and other high strength steels. In yet further embodiments, therotor 104 may be formed of any metal or metal alloy formulated towithstand a stress of at least 140 ksi (968 MPa) at a radial and axialcenter of the rotor 104.

In some embodiments, the rotor shaft 108 may be integrally formed withthe rotor disc 106 such that the rotor disc 106 and the rotor shaft 108form a single, monolithic unit. In other embodiments, the upper andlower shafts 108 a, 108 b may be separately formed (e.g., machined) andmay be fixed to the rotor disc 106 by, for example, welding. Without theupper and lower shafts 108 a, 108 b, the rotor disc 106 may have asubstantially uniform thickness T₁₀₆ across a diameter D₁₀₆. As usedherein, the term “disc” means and includes a cylindrical body having adiameter greater than a thickness. The thickness T₁₀₆ of the rotor disc106 may be in a range extending from about 6 inches to about 18 inches,and, more particularly, may be about 12 inches (e.g., 12.2 inches). Thediameter D₁₀₆ of the rotor disc 106 may be in a range extending fromabout 48 inches to about 96 inches and, more particularly, may be about80 inches. A weight of the rotor 104 may be in a range extending fromabout 12,000 pounds to about 18,000 pounds and, more particularly, maybe about 15,000 pounds or about 17,000 lbs (e.g., 17,200 lbs).

The system 100 further comprises an off-loading magnet 114 disposedwithin the housing 102. The off-loading magnet 114 may be coupled (e.g.,fixed) to an upper housing member 116. In some embodiments, theoff-loading magnet 114 may comprise an electromagnet configured to applyan axial force on the rotor 104 to attract (e.g., lift) the rotor 104upwards toward the upper bearing assembly 128 (e.g., in the axialdirection).

A first exterior housing 118 may be coupled to the upper housing member116 on an exterior of the housing 102. A motor/generator assembly 124may be disposed on (e.g., over) and may be coupled to the first exteriorhousing 118. An upper bearing assembly 128 may be disposed within thefirst exterior housing 118. A lower bearing assembly 130 may be coupledto a lower housing member 124 on an exterior of the housing 102. A geardrive system 126 may be coupled to the lower bearing assembly 130.

In some embodiments, the rotor 104 may comprise at least one groove 111sized and configured to receive one or more weights to balance the rotor104 for rotation with the housing 102. The groove 111 may extendannularly and proximate to the periphery of the rotor disc 106 in theupper surface 103 and/or the lower surface 105. The rotor 104 may bebalanced after assembly of the rotor 104 with the journal assemblies 200a, 200 b within the housing 102. Accordingly, as illustrated in thepartial, cross-sectional view of the housing 102 in FIG. 2 , the housing102 may comprise one or more flanged openings 113 through which weightsmay be passed to be disposed within the grooves 111. The system 100 mayfurther comprise at least one accelerometer coupled to and/or disposedabout a periphery of bearings 136 (FIGS. 3 and 4 ) to measure a level ofimbalance of the rotor 104. A tachometer or other device may also beoperatively coupled to the rotor 104 and may be provided within thehousing 102 to measure the rotational speed of the rotor 104.Accordingly, amplitudes of acceleration measured by the accelerometerprovide information regarding a mass imbalance of the rotor disc 106when the rotational speed of the rotor 104 is measured by thetachometer. A location of the mass imbalance may be determined such thata weight may be placed within the groove 111 to balance the rotor 104.Markings may be provided, such as angular degree markings, on the upperand lower surfaces 103, 105 of the rotor 104 to identify properplacement of the weights. By way of non-limiting example, degreemarkings in intervals of 5 degrees may be provided on the upper surface103 and/or the lower surface 105 of the rotor 104. Balancing the rotor104 reduces potential damage to the rotor 104 due to flywheelimbalances, such as rotor oscillation and vibration, and premature wearon the bearings 136 that may result from such imbalances. Overall,balancing the rotor 104 may extend the usable life of the flywheelsystem 100.

FIGS. 3 and 4 are enlarged cross-sectional views of an upper bearingassembly 128 and a lower bearing assembly 130, respectively, of FIG. 1 .The upper and lower bearing assemblies 128, 130 are operatively coupledto the rotor 104 at the respective upper and lower shafts 108 a, 108 b.

With continued reference to FIG. 3 , the upper bearing assembly 128comprises an outer housing 132 and an inner housing 134. The outerhousing 132 extends about (e.g., encircles) the inner housing 134. Theouter housing 132 may be stationary and may be fixed (e.g., coupled to)the upper housing member 116. The inner housing 134 may be axiallytranslatable (e.g., movable) within the outer housing 132. One or moresealing elements may be provided about the inner housing 134 and betweenthe inner housing 134 and the outer housing 132 to inhibit fluid fromflowing into the housing 102 from the upper bearing assembly 128. One ormore fastening elements, such as pins or dowels, may be provided betweenthe inner housing 134 and the outer housing 132 to inhibit rotation ofthe inner housing 134 relative to the outer housing 132. Bearings 136may be disposed within (e.g., encircled by) the inner housing 134 andabout the upper journal assembly 200 a.

The bearings 136 may comprise mechanical bearings such as ball bearingsincluding a plurality of balls within a raceway. In some embodiments,the upper and lower bearing assemblies 128, 130 may each comprise asingle ball bearing that includes a plurality of bearing elements (e.g.,ball bearings) within a raceway. In other embodiments, the upper andlower bearing assemblies 128, 130 may each comprise two or more bearingassemblies stacked axially adjacent to each other. The bearings 136 maycomprise angular contact bearings configured to support radial and axialloads during operation of the flywheel system 100.

A plate 138 may be disposed on a first, upper end 139 of the outerhousing 132. A thrust plate 140 may disposed at a first, upper end 142of the inner housing 134. A load cell 144 may be disposed axiallybetween the plate 138 and the thrust plate 140. The thrust plate 140 maybe axially translatable with the inner housing 134 and may apply a forceagainst the load cell 144 when the rotor 104 is lifted during operationsuch that the load cell 144 is located and configured to measure a forceapplied on the bearings 136 in the upper bearing assembly 128 duringoperation of the system 100. A sealing plate 147 may be disposed on asecond, lower end 145 of the inner housing 134. The sealing plate 147 islocated and configured to provide a seal between a vacuum environmentwithin the housing 102 and an atmospheric environment within the upperbearing assembly 128 and to seal fluid within the upper bearing assembly128 such that the fluid does not flow into the housing 102.

A fluid circulation system may be coupled to at least one of the upperbearing assembly 128 and the lower bearing assembly 130. The fluidcirculation system is configured to provide a fluid such as oil to thebearings 136 for lubrication and to provide fluid flow between the outerhousing 132 and the inner housing 134 of the upper bearing assembly 128(FIG. 3 ) and between an outer housing 170 and an inner housing 172 ofthe lower bearing assembly 130 (FIG. 4 ) for damping vibrations that mayresult from imbalance of the flywheel rotor 104 during operation of theflywheel system 100.

With reference to FIG. 3 , the outer housing 132 and the inner housing134 may comprise a plurality of openings (e.g., apertures, channels,etc.) through which fluid may be circulated in the upper bearingassembly 128. The outer housing 132 comprises a first aperture 146located proximate to the first end 139 and extending from an exteriorsurface of the outer housing 132 to a first channel 148. The firstchannel 148 extends axially within the outer housing 132 between thefirst aperture 146 and a second aperture 150. The second aperture 150 islocated between (e.g., intermediate) the first end 139 and a second,opposite end 141 of the outer housing 132. The first and secondapertures 146, 150 are located at opposing ends of the first channel 148such that the first aperture 146, the first channel 148, and the secondaperture 150 are in fluid communication with a fluid inlet 152 throughwhich fluid may be introduced into the upper bearing assembly 128.

The outer housing 132 comprises a plurality of third apertures 154located proximate to the second end 141 and extending from the interiorsurface of the outer housing 132 to a sump 156. The third apertures 154may be spaced circumferentially about the outer housing 132. The sump156 comprises a cavity extending annularly within the outer housing 132.A second channel 158 extends axially within the outer housing 132between the sump 156 and the first end 139. A fourth aperture 160 islocated proximate to the first end 139 and extends from the secondchannel 158 to the exterior surface of the outer housing 132. The thirdapertures 154, the sump 156, the second channel 158, and the fourthaperture 160 may be in fluid communication such that fluid flowing intothe sump 156 through the third apertures 154 may be removed by ascavenge pump, which may be coupled to the sump 156, from the sump 156through the second channel 158, the fourth aperture 160, and a fluidoutlet 168.

The inner housing 134 comprises a first groove 162 extending annularlyabout the exterior surface thereof and located proximate to the firstend 142. A plurality of first apertures 164 extends through the innerhousing 134 between the first groove 162 and an interior surface of theinner housing 134. The first apertures 164 may be circumferentiallyspaced about the inner housing 134. A plurality of second apertures 166may be provided proximate to the second end 145 of the inner housing 134and extend between the interior surface and the exterior surface of theinner housing 134. A second groove 163 extends annularly about theexterior surface thereof located proximate to the second end 141. Thesecond groove 163 is in fluid communication with the second apertures166. The inner housing 134 is located within the outer housing 132 suchthat the first groove 162 may be substantially aligned and in fluidcommunication with the second aperture 150 of the outer housing 132 andsuch that the second apertures 166 of the inner housing 134 are in fluidcommunication with the third apertures 154 of the outer housing 132.

In operation, fluid may be provided to the bearings 136 for lubricationby introducing fluid into the fluid inlet 152, through the firstaperture 146, the first channel 148, and the second aperture 150 of theouter housing 132, and radially inward from the second aperture 150 tothe first groove 162 and the first apertures 164 of the inner housing134. The first apertures 164 are located axially above the bearings 136such that fluid flows into the bearings 136 and through the bearings 136to impinge against the sealing plate 147. Fluid is diverted radiallyoutward on the sealing plate 147 to the second apertures 166, throughthe third apertures 154, and into the sump 156.

Further, the inner housing 134 and the outer housing 132 are sized andconfigured to provide fluid flow therebetween. A portion of the innerhousing 134 and the outer housing 132 encircling the bearings 136 may besized and configured such that a fluid may flow in an annular spacebetween the inner housing 134 and the outer housing 132 and form a fluidfilm of a squeeze film damper. The annular space may extend radiallybetween the inner housing 134 and the outer housing 132 and axiallybetween the first groove 162 and the second groove 163 of the innerhousing 134. In operation, fluid may be introduced into the fluid inlet152, through the first aperture 146, the first channel 148, and thesecond aperture 150 of the outer housing 132, from the second aperture150 to the first groove 162, axially from the first groove 162 to thesecond groove 163, and into the sump 156 through the third apertures 154of the outer housing 132. In some embodiments, a diameter of the firstapertures 164 may be selected to restrict (e.g., constrict) a rate offluid flow through therethrough and to build up fluid pressure upstreamfrom the first apertures 164, such as within the first groove 162 andthe first channel 148. In other embodiments, a fluid flow limitingdevice, such as a nozzle, may be provided within the first apertures 164to constrict fluid flow therethrough and to build up fluid pressureupstream from the first apertures 164. The diameter of the firstapertures 164 and/or the fluid flow limiting device is selected suchthat the rate at which fluid is provided (e.g., flow rate) through thefluid inlet 152 is greater than the rate at which the fluid is providedthrough the first apertures 164 and into the bearings 136.

Squeeze film damping occurs when force associated with radial and/oraxial vibration is transmitted from an upper journal assembly 200 a tothe bearings 136 and to the fluid film between the housings 132, 134.The fluid film exerts an opposing force to any radial and/or axialvibration in order inhibit (e.g., dampen or attenuate) vibrations. Inaddition, the fluid film provides a radial force on the bearings 136 andthe upper journal assembly 200 a to radially center rotation of theupper journal assembly 200 a. Accordingly, a common fluid circulationsystem is provided to lubricate the bearings 136 and to dampenvibrations during operation of the flywheel system 100 reducingpremature wear of bearings 136. Inhibiting deviations of the axis 112about which the rotor 104 rotates and damping vibrations results in anincreased usable life of the flywheel system 100. The fluid (e.g., oil)selected to flow through the upper bearing assembly 128 is selected tohave a viscosity extending in a range from about 5 centistokes (cSt) toabout 50 cSt as the fluid flows within the bearings 136 and a viscosityextending in a range from about 5 cSt to about 30 cSt as the fluid flowsbetween the housings 132, 134.

With reference to FIG. 4 , similar to the upper bearing assembly 128,the lower bearing assembly 130 comprises the outer housing 170 extendingabout the inner housing 172. The outer housing 170 may be stationary andfixed to the lower housing member 124. The inner housing 172 may beaxially translatable within the outer housing 170. One or more sealingelements may be provided about the inner housing 172 and between theinner housing 172 and the outer housing 170 to inhibit fluid fromflowing into the housing 102 from the lower bearing assembly 130. One ormore fastening elements may be provided between the inner housing 172and the outer housing 170 to inhibit rotation of the inner housing 172relative to the outer housing 170. Bearings 136 may be disposed withinthe inner housing 172 and about the lower journal assembly 200 b.

A first sealing plate 176 may be disposed on a first, upper end 175 ofthe inner housing 172, and a second sealing plate 179 may be disposed ona second, lower end 177 of the inner housing 172. The first sealingplate 176 is located and configured to seal the vacuum environmentwithin the housing 102 from an atmospheric environment within the lowerbearing assembly 130. The second sealing plate 179 is located andconfigured to seal fluid within the lower bearing assembly 130 such thatfluid does not flow into the gear drive system 126. The gear drivesystem 126 may be disposed adjacent to the second end 177 of the innerhousing 172. The gear drive system 126 comprises a stepper motor 180that is coupled to a center pinion 183. The center pinion 183 isthreadedly engaged with gears 181. One or more shafts 187 may extendbetween and be engaged with the gears 181 and the thrust plate 178. Aload cell 174 may be located between the second sealing plate 179 andthe thrust plate 178. The load cell 174 is located and configured tomeasure a force applied on the bearings 136 in the lower bearingassembly 130 during operation of the system 100. The gear drive system126 may be configured to adjust a load applied to bearings 136. Thestepper motor 180 may rotate the center pinion 183 such that rotation ofthe center pinion 183 rotates the gears 181. Rotation of the gears 181axially raises or lowers the shafts 187 engaged therewith, and theshafts 187 raise or lower the thrust plate 178 accordingly. Raising thethrust plate 178 may apply an axially upward force to the load cell 174of the lower bearing assembly 130.

The fluid circulation system may be further coupled to the lower bearingassembly 130. The outer housing 170 and the inner housing 172 maycomprise a plurality of openings through which fluid may be circulatedin the lower bearing assembly 130. The outer housing 170 comprises afirst aperture 182 located proximate to a first, lower end 171 andextending from an exterior surface of the outer housing 170 to a firstchannel 184. The first channel 184 extends axially within the outerhousing 170 between the first aperture 182 and a second aperture 186.The second aperture 186 is located proximate to a second, upper end 173of the outer housing 170. The first and second apertures 182, 186 arelocated at opposing ends of the first channel 184 such that the firstaperture 182, the first channel 184, and the second aperture 186 are influid communication with a fluid inlet 185 through which fluid may beintroduced into the lower bearing assembly 130. A third aperture 188 islocated proximate to the first end 171 and extends from the interiorsurface to the exterior surface of the outer housing 170.

The inner housing 172 comprises a first groove 190 extending annularlyabout the exterior surface and located proximate to the first end 175. Aplurality of first apertures 192 extends through the inner housing 172between the first groove 190 and an interior surface. A second groove191 extends annularly about the exterior surface of the inner housing172 and is located between the first end 175 and the second end 177 ofthe inner housing 172. The second groove 191 is in fluid communicationwith a plurality of second apertures 194. The second apertures 194extend through the inner housing 172 between the second groove 191 andthe interior surface. The first and second apertures 192, 194 may bespaced circumferentially about the inner housing 172. A third aperture196 may be provided that extends through the inner housing 172 adjacentthe second end 177 thereof. The inner housing 172 is located in theouter housing 170 such that the first groove 190 is in fluidcommunication with the second aperture 186 of the outer housing 170 andsuch that the third aperture 196 of the inner housing 172 is in fluidcommunication with the third aperture 188 of the outer housing 170.

In operation, fluid may be provided to the bearings 136 for lubricationthereof by introducing fluid into the fluid inlet 185 and through thefirst aperture 182, the first channel 184, and the second aperture 186of the outer housing 170 and through the second aperture 194, to thefirst groove 190 and the first apertures 192 of the inner housing 172.The inner housing 172 and the outer housing 170 may be located such thatthe first apertures 192 are located axially above the bearings 136 toprovide fluid flow into the bearings 136 and through the bearings 136 toimpinge against the second sealing plate 179. Fluid is diverted radiallyoutward on the second sealing plate 179 to the third aperture 196 of theinner housing 172, to the third aperture 188 of the outer housing 170,and to a fluid outlet 198.

The inner housing 172 and the outer housing 170 are further sized andconfigured to provide fluid flow therebetween to form a squeeze filmdamper about the bearings 136 of the lower bearing assembly 130 aspreviously discussed with respect to the upper bearing assembly 128. Aportion of the inner housing 172 and the outer housing 170 encirclingthe bearings 136 may be sized and configured such that an annular spacefor fluid flow is provided therebetween. The annular space may beprovided radially between the inner housing 172 and the outer housing170 and axially between the first groove 190 and the second groove 191of the inner housing 172. Accordingly, fluid may be introduced into thefluid inlet 185, through the first aperture 182, the first channel 184,and the second aperture 186 of the outer housing 170, from the secondaperture 186 to the first groove 190, axially from the first groove 190to the second groove 191, through the second apertures 194 radiallyinward through the inner housing 172, impinging against the secondsealing plate 179, and radially outward through the third aperture 196,the third aperture 188, and the fluid outlet 198. As previouslydescribed with reference to the first apertures 164, the first apertures192 may be selected to have a diameter and/or may include a fluid flowlimiting device that restricts fluid flow therethrough and into thebearings 136 and to build up fluid pressure upstream from the firstapertures 192, such as in the first groove 190 and/or the first channel184.

With reference to each of FIGS. 3 and 4 , the upper bearing assembly 128and the lower bearing assembly 130 surround (e.g., encircle) at least aportion of the upper journal assembly 200 a and the lower journalassembly 200 b, respectively. The upper and lower journal assemblies 200a, 200 b are separable from and coupled to the rotor 104. FIG. 5 is aperspective view of a journal assembly 200 for use in the upper andlower bearing assemblies 128, 130. FIGS. 6 and 7 respectively illustratea perspective view of a rod 202 and a sleeve 204, respectively, of thejournal assembly 200 when the journal assembly 200 is disassembled. Theupper and lower journal assemblies 200 a, 200 b may be provided forrotation with the flywheel rotor 104 and rotates within the upper andlower bearing assemblies 128, 130.

With continued reference to FIGS. 5 through 7 , each journal assembly200 may comprise a rod 202, a sleeve 204, and a retaining element 206.As best illustrated in FIG. 6 , the rod 202 may comprise a monolithicunit including a head 208, an elongated shaft 210, and an annular flange212 between the head 208 and the elongated shaft 210. The head 208 maybe located at a first end 214 of the rod 202, and one or more connectingelements 216 (e.g., threading) may be located proximate to a second,opposite end 218 of the rod 202. The connecting elements 216 may beprovided to couple the rod 202 and the retaining element 206. Theretaining element 206 may be a nut and/or may comprise correspondingthreading or other connecting features.

The flange 212 extends radially beyond an outer surface of the elongatedshaft 210 and the head 208. In some embodiments, and as best illustratedin FIG. 6 , a perimeter of the flange 212 may be polygonal in shape. Forexample, the flange 212 may be hexagonal in shape. A perimeter of atleast one of the protruding features 107 a, 107 b of the shafts 108 a,108 b may also be a polygonal shape and may have a corresponding numberof sides as the polygon shape of the flange 212. In some embodiments,the flange 212 may comprise at least one aperture 213 extendingtherethrough, and the shafts 108 a, 108 b may include a plurality ofrecesses therein. During assembly of the journal assembly 200 with therotor 104, the apertures 213 of the flange 212 may be aligned withrecesses in the shafts 108 a, 108 b to properly orient (e.g., align) thesides of the polygonal shape of the flange 212 and the protrudingfeatures 107 a, 107 b. A mechanical fastener may be provided in theapertures 213 of the flange 212 and the recesses of the protrudingfeatures 107 a, 107 b to assist in alignment of the rod 202 to the rotor104.

As best illustrated in FIG. 7 , the sleeve 204 may comprise a monolithicunit including an elongated (e.g., axially extending) shaft 220 and anenlarged head 222 extending axially and radially from the shaft 220. Thesleeve 204 may further comprise an aperture 224 extending axiallytherethrough from a first end 226 to a second, opposite end 228. Theaperture 224 of the sleeve 204 is sized and configured to receive atleast a portion of the rod 202 therein. The sleeve 204 includes one ormore connecting elements 216 located proximate to the second end 228.Such connecting elements 216 may be provided to operatively couple thesleeve 204 of the upper journal assembly 200 a to the motor/generatorassembly 124.

A portion of the aperture 224 within the head 222 of the sleeve 204 maybe complementary in shape to the protruding features 107 a, 107 b of therotor shaft 108. Accordingly, an interior surface of the sleeve 204defining a portion of the aperture 224 within the head 222 may bepolygonal in shape corresponding to the polygonal shape of the flange212 and the protruding features 107 a, 107 b. The corresponding shapesof the flange 212, the aperture 224, and the protruding features 107 a,107 b inhibits rotation of the rod 202, the sleeve 204, and the rotor104 relative to each other during operation of the flywheel system 100.

When the rod 202 and the sleeve 204 of the upper and lower journalassemblies 200 a, 200 b are assembled, as best illustrated in FIGS. 3through 5 , the elongated shaft 210 extends through the aperture 224 ofthe sleeve 204. As assembled, a longitudinal axis extending centrallythrough the aperture 224 of the sleeve 204 between the first and secondends 226, 228 thereof and a longitudinal axis extending centrallythrough the rod 202 between the first and second ends 214, 218 may becoaxial. A substantial portion (e.g., majority) of the shaft 210 of therod 202 may be retained within and encircled by the shaft 220 of thesleeve 204. The rod 202 may have a length greater than the sleeve 204.Accordingly, the rod 202 may be disposed within the sleeve 204 such thatat least a portion of the shaft 210 may extend axially beyond the secondend 228 of the sleeve 204 when the rod 202 is disposed therein and suchthat the connecting elements 216 are accessible and not surrounded bythe shaft 220. A sliding clearance fit may be provided between the shaft210 of the rod 202 and the shaft 220 of the sleeve 204 within theaperture 224 along a majority of the length of the shafts 210, 220. Aslip fit may be provided between the shaft 210 of the rod 202 and theshaft 220 of the sleeve 204 at the second ends 218, 228 of the shafts210, 220 adjacent to which the retaining element 206 is provided.Providing the rod 202 having a length greater than the length of thesleeve 204 inhibits deflection of the rod 202 within the sleeve 204,such as tilting of the longitudinal axis of the rod 202 relative to thelongitudinal axis of the sleeve 204 and/or the central axis 112 of therotor 104, and prevent the generation of a bending stress within the rod202 during operation of the system 100.

When assembled with the sleeve 204, the rod 202 may be held in tensionand, accordingly, may be referred to as a “tension rod.” In someembodiments, the tensioning force is applied to the rod 202 when the rod202 is disposed within the sleeve 204. A tensioning force may be appliedto the rod 202 by mechanically pulling axially on the second end 218 ofthe rod 202. A compressive force may be applied to the sleeve 204 whilethe tensioning force is applied to the rod 202. The first end 214 of therod 202 may be disposed in the recesses 103 a, 103 b of the rotor shaft108 while the tensioning force is applied to the second end 218 of therod 202. The tensioning force may be applied until a tension forcemeasured in the rod 202 is in a range extending from about 10,000 lbf toabout 20,000 lbf such as about 12,000 lbf. When the desired tensionforce is measured in the rod 202, the compressive force on the sleeve204 is released, and the retaining element 206 may be coupled to the rod202. The retaining element 206 maintains the tension force within therod 202 during operation of the flywheel system 100. The tension forcewithin the rod 202 may inhibit tilting of the rod 202 relative to thesleeve 204 such that the rod 202 and the sleeve 204 are maintained in acoaxial arrangement during operation of the system 100. The tensionforce in the rod 202 may also increase the rigidity of the journalassemblies 200 a, 200 b and further inhibit wobbling (e.g., tilting) ofthe journal assemblies 200 a, 200 b relative to the rotor 104.

When the journal assemblies 200 a, 200 b are assembled with the rotor104, as best illustrated in FIGS. 3 and 4 , the rod 202 may be coupled(e.g., fastened) to the rotor 104. In some embodiments, the upper andlower shafts 108 a, 108 b include respective upper and lower recesses103 a, 103 b formed therein for coupling the rod 202 to the rotor 104.The recesses 103 a, 103 b are sized and configured to receive the head208 of a rod 202 of the journal assemblies 200 a, 200 b, respectively,therein. More particularly, the recesses 103 a, 103 b are sized andconfigured to retain the head 208 of the rod 202 therein by mechanicalinterference, or an interference fit and, more particularly, by a pressfit. Alternatively or additionally, inner surfaces of the shafts 108 a,108 b within the recesses 103 a, 103 b may comprise with one or morecoupling features such as threading thereon, and an outer surface of thehead 208 of the rod 202 may comprise corresponding coupling featuressuch that the head 208 of the rod 202 may be retained in the rotorshafts 108 a, 108 b. The bearings 136 may be retained about the sleeve204 by a threadless connection such as by press fit.

As further illustrated in FIGS. 3 and 4 , the sleeve 204 may be coupledto the rotor 104. When the sleeve 204 is assembled with the rotor 104,at least a portion of the head 222 of the sleeve 204 may extend about(e.g., encircle) the protruding features 107 a, 107 b of the shafts 108a, 108 b. The protruding features 107 a, 107 b of the shafts 108 a, 108b and the flange 212 of the rod 202 may be disposed within a portion ofthe aperture 224 within the head 222 of the sleeve 204. Accordingly, theflange 212 may be disposed axially between the sleeve 204 and the rotor104. The aperture 224 is sized and configured such that the head 222 ofthe sleeve 204 may be coupled to the shafts 108 a, 108 b by mechanicalinterference (e.g., an interference fit), such as a press fit.Interference fit between the sleeve 204 and the rod 202 inhibitswobbling of the sleeve 204 and the rod 202 relative to each other andrelative to the rotor 104 and maintains the sleeve 204 and the rod 202such that the sleeve 204 and the rod 202 are arranged coaxially. Thehead 222 of the sleeve 204 may be disposed circumferentially about theprotruding features 107 a, 107 b and the head 222 applies a radiallycompressive force on the protruding features 107 a, 107 b. The radiallycompressive force couples the sleeve 204 to the rotor 104, inhibitsrotation of the sleeve 204 relative to the rotor 104, and/or inhibitswobbling (e.g., inclining of the rotor 104 along an axis transverse tothe axis 112) of the rotor 104 relative to the assemblies 200 a, 200 bduring operation of the flywheel system 100. The radially compressiveforce is selected to limit inclining of the sleeve 204 relative to therotor 104 to about 0.000001 inch. The radially compressive force may beselected to extend in a range from about 500 lbf to about 1500 lbf, suchas about 1025 lbf. As assembled, the longitudinal axes of the sleeve 204and the rod 202 and the axis 112 of the rotor 104 may be coaxial.

With continued reference to FIGS. 3 and 4 , a seal runner 231 may beprovided about the sleeve 204 and may be configured to inhibit axialmovement of the bearings 136 along the sleeve 204. The seal runner 231may be disposed axially between the bearings 136 and the head 222 of thesleeve 204. The seal runner 231 may be disposed radially between thesleeve 204 and the respective sealing plates 147, 179 of the upper andlower bearing assemblies 128, 130. The seal runner 231 may be retainedabout the sleeve 204 by a threadless connection such as by a press fit.A seal 232 may be provided about the sleeve 204 and compressed betweenthe seal runner 231 and the shaft 220. The seal 232 may comprise ano-ring, washer, or other element configured to inhibit (e.g., prevent)fluid flow from the bearings 136 from flowing between the seal runner231 and the sleeve 204 and into the housing 102.

In operation, the motor/generator 124 is coupled to the rotor 104 by theupper journal assembly 200 a and is configured to convert electricalenergy into rotational kinetic energy by inputting energy into thesystem 100 to spin (e.g., rotate) the rotor 104 and/or to convertrotational kinetic energy of the rotor 104 into electrical energy.Accordingly, energy can be stored in and/or drawn from the rotor 104. Torotate the rotor 104, the rotor 104 may be lifted using the off-loadingmagnet 114. When the rotor 104 is at least, the weight of the rotor 104is supported by the bearings 136 of the lower bearing assembly 130. Insome embodiments, a current is provided to the off-loading magnet 114 togenerate a magnetic force that is applied to the rotor 104 to provide anaxial lifting force (e.g., in a direction parallel to the axis 112 ofthe rotor 104) on the rotor 104 toward the upper housing member 116.

Initially, a current is applied to the off-loading magnet 114 sufficientto levitate the rotor 104 within the housing 102 such that substantiallyno axial force (e.g., force measured in a direct parallel to the axis112) is applied by the rotor 104 on the bearings 136. While levitatingthe rotor 104 within the housing 102 throughout the flywheel operationmay maximize the efficiency of the flywheel system 100 by reducingfriction losses in the system 100, a force may be applied by the rotor104 on the bearings 136 to inhibit balls in the bearings 136 fromskidding is not feasible throughout operation. Accordingly, the currentapplied to the off-loading magnet 114 may be adjusted during operationof the rotor 104 to maintain a pre-determined load on the bearings 136in the upper bearing assembly 128. Additionally, the gear drive system126 coupled to the lower bearing assembly 130 may be adjusted duringoperation of the rotor 104 to maintain a pre-determined load on thebearings 136 in the lower bearing assembly 130. In some embodiments, thepre-determined force applied to the bearings 136 of the upper and lowerbearing assemblies 128, 130 and measured by the load cells 144, 174 isselected to be substantially equal. In other embodiments, a differentialforce may be applied to the bearings of the upper and lower bearingassemblies 128, 130. For example, a load in a range extending from about100 lbs and about 500 lbs or about 300 lbs may be applied to each of thebearings 136 and measured by the respective load cells 144, 174.

A load may be applied to the bearing 136 and measured by the load cell144 in the upper bearing assembly 128 by axially translating the rotor104 with the off-loading magnet 114 and by compressing one or morecomponents of the upper journal assembly 200 a and the upper bearingassembly 128 between the rotor 104 and the plate 138 of the outerhousing 132. As the rotor 104 is lifted, the seal runner 231, thebearing 136, the inner housing 134, the thrust plate 140, and the loadcell 144 are lifted correspondingly with the upper journal assembly 200a that is coupled to the rotor 104. As the components of the upperbearing assembly 128 are axially translated within the stationary outerhousing 132, the load cell 144 is compressed between the thrust plate140 and the plate 138. When the load cell 144 is compressed and a loadis measured by the load cell 144, a compressive force may be applied onand between axially adjacent components of the upper bearing assembly128. Accordingly, the rotor 104 may apply a compressive force on thesleeve 204, the sleeve 204 may apply a compressive force on the sealrunner 231, the seal runner 231 may apply a compressive force on theraceway of the bearing 136, the raceway of the bearing 136 may apply acompressive force on the inner housing 134, the thrust plate 140 mayapply a compressive force on the load cell 144, and the load cell 144may apply a compressive force on the plate 138. Each of the foregoingcompressive forces may be applied in the axial direction parallel to thecentral axis 112.

A load may be applied to the bearing 136 and measured by the load cell174 in the lower bearing assembly 130 by axially translating the thrustplate 178 of the gear drive system 126 and by compressing one or morecomponents of the lower journal assembly 200 b and the lower bearingassembly 130 between the rotor 104 and the thrust plate 178 fixed to thegear drive system 126. In the gear drive system 126, the stepper motor180 may rotate the center pinion 183 such that the gears 181 arerotated. Rotation of the gears 181 is converted into axial movement ofthe shafts 187 operatively coupled to the gears 181. Axial movement ofthe shafts 187 raises or lowers the thrust plate 178 along the centralaxis 112. As the thrust plate 178 is lifted, the lower journal assembly200 b and one or more components of the lower bearing assembly 130 arelifted correspondingly. As the thrust plate 178 is lifted, the load cell174, the first sealing plate 176, the inner housing 172, the bearings136, the seal runner 231, and the sleeve 204 are lifted correspondinglyand are axially translated within the stationary outer housing 170 suchthe load cell 174 is compressed between the thrust plate 178 and thesecond sealing plate 179. When the load cell 174 is compressed and aload is measured by the load cell 174, a compressive force may beapplied on and between axially adjacent components of the lower bearingassembly 130. In such embodiments, the-second sealing plate 179 mayapply a compressive force on the inner housing 172, the inner housing172 may apply a compressive force on the race way of the bearing 136,the raceway of the bearing 136 may apply a compressive force on the sealrunner 231, the seal runner 231 may apply a compressive force on thesleeve 204, and the sleeve 204 may apply a compressive force on therotor 104. Each of the foregoing compressive forces may be applied inthe axial direction parallel to the central axis 112.

In some embodiments, the gear drive system 126 and the off-loadingmagnet 114 are coupled to at least one controller that monitors (e.g.,measures) a load measured by the load cells 144, 174 and, based on theload measured, may adjust the current applied to the off-loading magnet114 and/or the axial position of the thrust plate 178 such that apredetermined load is applied to the load cells 144, 174. In someembodiments, the gear drive system 126 and the off-loading magnet 114may be coupled to separate controllers. The gear drive system 126 andthe off-loading magnet 114 may be separately adjustable. The controllermay employ a feedback control loop, such as aproportional-integral-derivative (PID) control loop. The PID controlloops accounts for a current state of the flywheel system 100 (e.g.,current load on load cells 144, 174) in relation to a desired setpoint,or the predetermined load (proportional), the accumulation of past errorin the flywheel system 100 (integral) and a prediction of future errorof the flywheel system (derivative) to adjust or to maintain a currentapplied to the off-loading magnet 114 and/or to adjust or to maintain aposition of the thrust plate 178.

While the present invention has been described herein with respect tocertain illustrated embodiments, those of ordinary skill in the art willrecognize and appreciate that it is not so limited. Rather, manyadditions, deletions, and modifications to the illustrated embodimentsmay be made without departing from the scope of the invention ashereinafter claimed, including legal equivalents thereof. In addition,features from one embodiment may be combined with features of anotherembodiment while still being encompassed within the scope of theinvention as contemplated by the inventors.

What is claimed is:
 1. A flywheel system, comprising: a flywheel rotorcomprising a rotor disc and a rotor shaft; and a journal assemblyadjacent to the flywheel rotor and comprising: a sleeve having anaperture extending therethrough from a first end to an opposite secondend, the second end of the sleeve coupled to the rotor shaft; and a rodat least partially disposed within the aperture of the sleeve, the rodcomprising an elongated shaft at a first end thereof and a head at asecond end thereof, the first end of the rod extending axially beyondthe first end of the sleeve, and the head at the second end of the rodretained by mechanical interference within a recess in the rotor shaft,wherein longitudinal axes of the sleeve and the rod are coaxial with alongitudinal axis of the flywheel rotor.
 2. The flywheel system of claim1, wherein the rod comprises an annular protrusion between the elongatedshaft and the head, the annular protrusion extending circumferentiallybeyond outer surfaces of the elongated shaft and the head.
 3. Theflywheel system of claim 2, wherein the annular protrusion of the rodintervenes between a portion of the sleeve and the rotor shaft.
 4. Theflywheel system of claim 2, wherein the rotor shaft comprises protrudingfeatures adjacent to the rod, outer surfaces of the annular protrusionof the rod comprising one or more linear portions corresponding to theprotruding features of the rotor shaft.
 5. The flywheel system of claim1, wherein the rod has a longitudinal length relatively greater than alongitudinal length of the sleeve, the second end of the rod extendingaxially beyond the second end of the sleeve.
 6. The flywheel system ofclaim 1, wherein the second end of the sleeve encircles an end portionof the rotor shaft, the second end of the sleeve coupled to the endportion of the rotor shaft by mechanical interference.
 7. The flywheelsystem of claim 1, wherein the sleeve and the rod individually comprisea single, monolithic unit.
 8. A flywheel system, comprising: a flywheelrotor comprising a rotor disc and a rotor shaft; a journal assemblyadjacent to the flywheel rotor and comprising: a sleeve having anaperture extending therethrough from a first end to an opposite secondend, the second end of the sleeve coupled to the rotor shaft; and a rodat least partially disposed within the aperture of the sleeve, a firstend of the rod extending axially beyond the first end of the sleeve anda second end of the rod coupled to the rotor shaft, and the rod having alongitudinal axis coaxial with longitudinal axes of the sleeve and theflywheel rotor; a bearing assembly encircling the journal assembly, thebearing assembly comprising bearings disposed between an inner housingand an outer housing; and an annular space extending radially betweenthe inner housing and the outer housing about the bearings, the annularspace sized and configured for formation of a squeeze film damper aboutthe bearings.
 9. The flywheel system of claim 8, wherein the innerhousing is movably disposed within the outer housing.
 10. The flywheelsystem of claim 8, wherein the outer housing substantially surrounds theinner housing, and the inner housing is coupled to the outer housing.11. The flywheel system of claim 8, wherein an exterior surface of theinner housing and an interior surface of the outer housing define atleast one fluid path of the annular space extending radially between theinner housing and the outer housing.
 12. The flywheel system of claim11, wherein at least one fluid path is in communication with thebearings of the bearing assembly.
 13. The flywheel system of claim 8,wherein the bearings comprise angular contact bearings configured tosupport one or more of radial loads and axial loads of the flywheelrotor.
 14. A flywheel system, comprising: a flywheel rotor comprising arotor disc and a rotor shaft; an upper journal assembly and a lowerjournal assembly coupled to the flywheel rotor, each of the upperjournal assembly and the lower journal assembly comprising: a sleevehaving an aperture extending therethrough from a first end to anopposite second end; a rod disposed within the aperture of the sleevesuch that a portion the rod extends axially beyond the first end of thesleeve; an upper bearing assembly disposed about the upper journalassembly; a lower bearing assembly disposed about the lower journalassembly; and an electromagnet adjacent to the rotor disc, theelectromagnet configured to move the flywheel rotor axially toward theupper bearing assembly and away from the lower bearing assembly to applyan axially compressive force against a bearing disposed within the upperbearing assembly.
 15. The flywheel system of claim 14, furthercomprising a gear drive system adjacent to the lower bearing assembly,the gear drive system and the electromagnet configured to adjust a loadapplied to the bearing.
 16. The flywheel system of claim 14, wherein theupper bearing assembly comprises a first load cell adjacent to the upperjournal assembly and the lower bearing assembly comprises a second loadcell adjacent to the lower journal assembly.
 17. The flywheel system ofclaim 14, wherein the sleeve is coupled to the rotor shaft, the secondend of the sleeve circumferentially enclosing an end of the rotor shaft.18. The flywheel system of claim 14, wherein the sleeve directlycontacts the rotor shaft along at least two consecutive sides of therotor shaft.
 19. The flywheel system of claim 14, wherein a longitudinalaxis of the flywheel rotor extends centrally through the rotor disc andthe rotor shaft, the longitudinal axis of the flywheel rotorsubstantially aligned with longitudinal axes of the sleeve and the rod.20. The flywheel system of claim 14, wherein: the upper bearing assemblycomprises two or more bearing assemblies stacked axially adjacent to oneanother; and the lower bearing assembly comprises two or more additionalbearing assemblies stacked axially adjacent to one another.